1. Technical Field of the Invention
The present invention relates to the field of integrated circuit chips equipped with projecting external contact pads.
2. Description of Related Art
Integrated circuit chips equipped with projecting external contact pads are intended in particular to be mounted on boards in such a way that their external contact pads make electrical connections on these boards. To do this, during the mounting operation, the chips are pressed onto boards provided with a dielectric layer having, in suspension, particles made of an electrically conducting material, in such a way that the particles located between the boards and the end or front faces of the external contact pads establish the electrical connections.
Currently, starting from a chip having a lower layer on which internal pads are formed and a surface layer that covers the latter and has surface bumps in the regions of these internal pads, apertures are produced in the surface layer, above the internal pads, and the projecting external contact pads are produced by a deposition process, whereby an electrically conducting material is grown in the apertures of the surface layer and in apertures of a temporary mask, which are wider than the apertures in the surface layer. As a result, the end faces of the external contact pads obtained have a central recessed portion and a peripheral rim corresponding to the rim of the surface layer surrounding the corresponding aperture made in this layer.
Such an arrangement results in a weakening of the surface layer around the external contact pads and a risk of cracks appearing during the aforementioned mounting operation, which must be carried out using relatively high pressures owing to the existence of said recessed portions, these cracks being favorable to the occurrence of internal corrosion of the chip. Furthermore, since the internal pads are in general made of aluminum and the external contact pads are in general made of gold, there is a risk of electrochemical reactions liable, by swelling of the material, to degrade the electrical connections and further increase the risk of cracks appearing.